Crankshaft for an internal combustion engine

ABSTRACT

A crankshaft for an internal combustion engine comprises at least four main journals aligned on a crankshaft axis of rotation and at least three crankpins, each disposed about a respective crankpin axis and positioned between the main journals. Each of the respective crankpin axes is oriented parallel to, and spaced radially from, the crankshaft axis of rotation. Each of the crankpins is joined to a pair of crank arms for force transmission between the crankpin and the pair of crank arms. Each pair of crank arms is joined to a respective main journal for transmitting torque between the pair of crank arms and the main journal. At least two of the crankpins are positioned substantially in phase with one another and a third crankpin being positioned approximately 180 degrees apart from the at least two crankpins.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/378,557 filed Aug. 31, 2010, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Exemplary embodiments of the invention relate to crankshafts forinternal combustion engines and, more particularly, to a crankshaft foran internal combustion engine having a grouping of three crankpins, inwhich two of the crankpins are disposed substantially in phase with oneanother and the third crankpin is disposed approximately 180 degreesapart from the other two crankpins.

BACKGROUND

With the increased focus on vehicle economy, particularly vehicle fueleconomy, automotive manufacturers are turning to smaller, lightervehicles and unique vehicle powertrains to boost efficiency.Recirculated exhaust gas (“EGR”) is utilized in most conventionalinternal combustion engines to assist in the reduction of throttlinglosses at low loads, and to improve knock tolerance and reduce the levelof oxides of nitrogen (“NO_(X)”) in the exhaust gas at high engineloads. EGR is especially important as an emissions reducer in internalcombustion engines that run lean of stoichiometry and thereby are proneto emitting higher levels of NO_(X) emissions.

One proposition that has been considered in the construction of internalcombustion engine systems is to utilize one of a plurality of cylindersas a dedicated EGR source. For example, in a four cylinder engine, theentire supply of exhaust gas produced in one of the cylinders istransferred to the intake ports of the other three cylinders as EGR. TheEGR-producing cylinder may be operated at customized levels of air andfuel; as may be determined by an engine controller that is in signalcommunication with various engine, vehicle and exhaust system sensors.Since the exhaust gas from the EGR-producing cylinder is to bere-circulated before being released to the atmosphere, the customizedair and fuel levels in the EGR-producing cylinder may be optimized toachieve selected goals such as engine efficiency, power, andoperability.

Since exhaust gas produced by the remaining two cylinders is to bereleased to the atmosphere following treatment in an exhaust gastreatment system, the air and fuel mixtures of these remaining cylindersare operated so as to meet emission standards. Fortuitously, theseremaining cylinders enjoy benefits associated with ingestion of EGR fromthe EGR-producing cylinder. These benefits include reduced combustiontemperatures and associated levels of NO_(X), allowing richer levels ofEGR in the remaining cylinders with increased levels of hydrogen,thereby improving knock resistance, fuel consumption and combustionstability, while still allowing stoichiometric gas to be maintained inthe exhaust gas treatment system for compatibility with the catalytictreatment devices.

A disadvantage to this type of internal combustion engine system is thatan internal combustion engine that uses only a single cylinder as thededicated EGR cylinder may not uniformly deliver EGR volumes to theremaining cylinders. For example, the cylinder event following thededicated EGR cylinder event may be prone to receive more EGR diluentthan the subsequently firing cylinders. This variation in cylindermakeup (i.e. combustion air, fuel and EGR diluent) can result in unevencombustion performance that is difficult to control over a broad rangeof operating conditions.

To at least partially address these disadvantages, a number ofconfigurations are being studied, including configurations wherein morethan one in four cylinders operates as a dedicated EGR cylinder or wherea dedicated EGR cylinder produces more than a single volume of exhaustgas for every four volumes of exhaust gas produced by other cylinders.To enable such configurations, it would be advantageous to have acrankshaft that can facilitate improved distribution of EGR amongnon-EGR cylinders.

SUMMARY

In an exemplary embodiment, a crankshaft for an internal combustionengine comprises at least four main journals aligned on a crankshaftaxis of rotation and at least three crankpins, each disposed about arespective crankpin axis and positioned between the main journals. Eachof the respective crankpin axes is oriented parallel to, and spacedradially from, the crankshaft axis of rotation. Each of the crankpins isjoined to a pair of crank arms for force transmission between thecrankpin and the pair of crank arms. Each pair of crank arms is joinedto a respective main journal for transmitting torque between the pair ofcrank arms and the main journal. At least two of the crankpins arepositioned substantially in phase with one another and a third crankpinbeing positioned approximately 180 degrees apart from the at least twocrankpins.

In an exemplary embodiment, a rotating group for an internal combustionengine comprises three pistons, each associated with a respectivecylinder and connected through a respective connecting rod to arespective crankpin, the crankpins being disposed on a singlecrankshaft. The crankshaft comprises at least four main journals alignedon a crankshaft axis of rotation and at least three crankpins, eachdisposed about a respective crankpin axis and positioned between themain journals. Each of the respective crankpin axes are orientedparallel to, and spaced radially from, the crankshaft axis of rotation.Each of the crankpins are joined to a pair of crank arms for forcetransmission between the crankpin and the pair of crank arms. Each pairof crank arms are joined to a respective main journal for transmittingtorque between the pair of crank arms and the main journal. At least twoof the crankpins are positioned substantially in phase with one another,and a third crankpin is positioned approximately 180 degrees apart fromthe at least two crankpins.

The above features and advantages, and other features and advantages ofthe invention are readily apparent from the following detaileddescription of the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, advantages and details appear, by way ofexample only, in the following detailed description of the embodiments,the detailed description referring to the drawings in which:

FIG. 1 is a schematic plan view of portions of an internal combustionengine system embodying features of the invention;

FIG. 2 is a schematic plan view of portions of an internal combustionengine system embodying features of another embodiment of the invention;

FIG. 3 is a schematic plan view of portions of an internal combustionengine system embodying features of another embodiment of the invention;

FIG. 4 is a schematic plan view of portions of an internal combustionengine system embodying features of another embodiment of the invention;

FIG. 5 is a schematic plan view of portions of an internal combustionengine system embodying features of another embodiment of the invention;

FIG. 6 is a schematic plan view of portions of an internal combustionengine system embodying features of another embodiment of the invention;

FIG. 7 is a graph depicting operation of an internal combustion enginesystem embodying features of an embodiment of the invention; and

FIG. 8 is a graph depicting operation of an internal combustion enginesystem embodying features of another embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is notintended to limit the present disclosure, its application or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Referring now to FIG. 1, an exemplary embodiment of the invention isdirected to an internal combustion engine system 10 comprising aplurality of engine cylinders 12. In the embodiment illustrated, theinternal combustion engine system 10 includes three engine cylinders 12,however the configuration may also include any number of cylinders (ex.3, 4, 5, 6, 8, 10, 12, etc.) as well as configurations such as in-line(shown), V-configured, horizontally opposed and the like, withoutaffecting the application of the invention thereto.

Referring to the engine cylinders 12 in the embodiment shown, the firstand third cylinders 14 are configured to operate on a four-strokecombustion cycle. Contrarily, the second cylinder 16 is a dedicated EGRcylinder and is configured to operate on a 2-stroke combustion cycle; aswill be described in further detail below. Combustion air 18 iscompressed by a compressor 20 which may comprise an engine drivensupercharger, an exhaust driven turbocharger or a combination of both(i.e. super-turbocharger) and is delivered to each of the enginecylinders 12 through a portion of an intake system 24 comprising intakerunners 26, 28 and 30. The intake runners 26, 28 and 30 deliver thecompressed combustion air to the 4-stroke cylinders 14 through intakeports 32 and to the 2-stroke cylinder through intake port or ports 34.The combustion air 18 is mixed with fuel in the cylinders 14 and 16, andis combusted therein. One or more ignition devices such as spark plugs36 are located in communication with the cylinders 14 and 16 and operateto ignite the fuel/air mixture therein.

In an exemplary embodiment, exhaust gas 38 from the combustion of fueland combustion air 18 in the 2-stroke, dedicated EGR cylinder 16 isremoved from the cylinder 16 through one or more exhaust ports 40 influid communication with an EGR supply conduit 42 extending between, andin fluid communication with, intake ports 44 that are configured todeliver the exhaust gas 38 to the 4-stroke cylinders 14 as recirculatedexhaust gas (“EGR”) 46. The recirculated exhaust gas 46 is mixed withthe combustion air 18 and fuel in each 4-stroke cylinder 14 prior tocombustion thereof. The EGR 46 supplied from the 2-stroke, dedicated EGRcylinder 16 to the 4-stroke cylinders 14 functions to assist in thereduction of throttling losses at low loads and to improve knocktolerance and reduce the level of oxides of nitrogen (“NO_(X)”) in theexhaust gas.

In an exemplary embodiment, one or more heat exchangers 48 may bedisposed between the 2-stroke, dedicated EGR cylinder 16 and the intakeports 44 of the 4-stroke cylinders 14 to cool the EGR charge 46 allowingfor a cooler and, thus, denser flow of EGR into the 4-stroke cylinders14. The heat exchangers 48 may be of an air cooled or liquid cooledconfiguration. In an exemplary embodiment, exhaust gas 50 from thecombustion of fuel, combustion air 18 and EGR 46 in the 4-strokecylinders 14 is removed from the cylinders through one or more exhaustports 52 in fluid communication with an exhaust gas treatment system 54that may include various exhaust gas treatment devices 56 such as acatalytic converter, a selective catalytic reduction device, aparticulate trap or a combination thereof.

Referring now to FIG. 2, another exemplary embodiment of the inventionis directed to an internal combustion engine system 10 comprising aplurality of engine cylinders 12. In the embodiment illustrated, theinternal combustion engine system 10 includes three engine cylinders 12,however the configuration may also include any number of cylinders (ex.3, 4, 5, 6, 8, 10, 12, etc.) as well as configurations such as in-line(shown), V-configured, horizontally opposed and the like, withoutaffecting the application of the invention thereto.

Referring to the engine cylinders 12 in the embodiment shown, the firstand third cylinders 14 are configured to operate on a four-strokecombustion cycle. Contrarily, the second cylinder 16 is a dedicated EGRcylinder and is configured to operate on a 2-stroke combustion cycle; aswill be described in further detail below. Combustion air 18 iscompressed by a compressor 20 which may comprise an engine drivensupercharger, an exhaust driven turbocharger or a combination of both(i.e. super-turbocharger) and is delivered to each of the enginecylinders 12 through a portion of an intake system 24 comprising intakerunners 26, 28 and 30. The intake runners 26, 28 and 30 deliver thecompressed combustion air to the 4-stroke cylinders 14 through intakeports 32 and to the 2-stroke cylinder through intake port or ports 34.The combustion air 18 is mixed with fuel in the cylinders 14 and 16, iscombusted therein. One or more ignition devices such as spark plugs 36are located in communication with the cylinders 14 and 16 and operate toignite the fuel/air mixture therein.

In an exemplary embodiment, exhaust gas 38 from the combustion of fueland combustion air 18 in the 2-stroke, dedicated EGR cylinder 16 isremoved from the cylinder through one or more exhaust ports 40 in fluidcommunication with an EGR supply conduit 42 extending between, and influid communication with, the intake port 80 of the compressor 20 and isconfigured to deliver the exhaust gas 38 to the compressor 20 formixture with the combustion air 18 and compression into combustioncharge 82. As a result, combustion charge 82 includes a mixture ofcombustion air 18 and recirculated exhaust gas 38 and is delivered tothe to the 4-stroke cylinders 14 through the intake runners 26, 28 andto the 2-stroke cylinder 16 through intake runner 30. The exhaust gas 38supplied from the 2-stroke, dedicated EGR cylinder 16 to the compressorintake port of the intake system 24 functions to assist in the reductionof throttling losses at low loads and to improve knock tolerance andreduce the level of oxides of nitrogen (“NO_(X)”) in the exhaust gas.

In an exemplary embodiment, a heat exchanger 48 may be disposed betweenthe exhaust port 40 of the 2-stroke, dedicated EGR cylinder 16 and thecompressor intake port 80 to cool the exhaust gas 38 allowing for acooler and, thus, denser flow of exhaust gas into the compressor 20. Theheat exchanger 48 may be of an air cooled or liquid cooledconfiguration. In an exemplary embodiment, exhaust gas 50 from thecombustion of fuel and the combustion charge 82 in the 4-strokecylinders 14 is removed from the cylinders through one or more exhaustports 52 in fluid communication with an exhaust gas treatment system 54that may include various exhaust gas treatment devices 56 such as acatalytic converter, a selective catalytic reduction device, aparticulate trap or a combination thereof.

In an exemplary embodiment, the 4- and 2-stroke cylinders 14, 16,respectively, interact with a rotating group that comprises, pistons(not shown) that are each associated with a respective cylinder andconnected through a respective connecting rod (not shown) to arespective crankpin, the crankpins being disposed on a singlecrankshaft. In an exemplary embodiment, as shown in FIG. 5 and FIG. 6, acrankshaft 100 for an internal combustion engine comprises a pluralityof main journals 110, 112, 114, 116 aligned on a crankshaft axis ofrotation 118. A first (i.e., outer) crankpin 120 is disposed about afirst crankpin axis 122 and positioned between a first main journal 110and a second main journal 112. A second (i.e., inner) crankpin 130 isdisposed about a second crankpin axis 132 and positioned between thesecond main journal 112 and a third main journal 114. A third (i.e.,outer) crankpin 140 is disposed about a third crankpin axis 142 andpositioned between the third main journal 114 and a fourth main journal116. Each crankpin 120, 130, 140 is aligned on a respective crankpinaxis 122, 132, 142 that is parallel to, and spaced radially from, thecrankshaft axis of rotation 118.

A first pair of crank arms 150 is joined to first crankpin 120 for forcetransmission between first crankpin 120 and the first pair of crank arms150. Each of the crank arms 150 is also joined to a respective mainjournal 110, 112 for transmitting torque between the first pair of crankarms 150 and the main journals 110, 112. A second pair of crank arms 152is joined to second crankpin 130 for force transmission between secondcrankpin 130 and the second pair of crank arms 152. Each of the crankarms 152 is also joined to a respective main journal 112, 114 fortransmitting torque between the second pair of crank arms 152 and themain journals 112, 114. A third pair of crank arms 154 is joined tothird crankpin 140 for force transmission between third crankpin 140 andthe third pair of crank arms 154. Each of the crank arms 154 is alsojoined to a respective main journal 114, 116 for transmitting torquebetween the third pair of crank arms 154 and the main journals 114, 116.

In an exemplary embodiment, the crankpins 120, 130, 140 form a crankpingrouping arranged to enable, with respect to their three associatedcylinders, a “near-even fire” combustion sequence. Thus, in the case ofthe 3-cylinder internal combustion engine 10, four nearly evenly spacedfiring events are produced in about 720 degrees of rotation of thecrankshaft. For example, in an engine configuration wherein a 2-strokecylinder is disposed between a pair of 4-stroke cylinders, such as inthe exemplary three cylinder internal combustion engines of FIG. 1 andFIG. 2, the first crankpin 120 is coupled, through a connecting rod (notshown), to a piston (not shown) that is disposed in a first one of thecylinders 14. That cylinder is configured to operate on a four-strokecombustion cycle. Thus, as crankshaft 100 rotates about the crankshaftaxis of rotation 118, the piston that is coupled to the first crankpin120 interacts with working fluid (i.e., fuel, air and EGR mixture) inthe first cylinder 14, which encounters a combustion event once forevery 720 degrees of crankshaft rotation.

Similarly, the third crankpin 140 is coupled, through a connecting rod(not shown), to a piston (not shown) that is disposed in another of thecylinders 14 configured to operate on a four-stroke combustion cycle.Thus, as crankshaft 100 rotates about the crankshaft axis of rotation118 (i.e., through its range of rotational crankshaft positions), thepiston that is coupled to the third crankpin 140 interacts with workingfluid (i.e., fuel, air and EGR mixture) in the third cylinder 14, whichalso encounters a combustion event once for every 720 degrees ofcrankshaft rotation.

In accordance with this embodiment, the crankpins for the 4-strokecylinders 14 (i.e., the first crankpin 120 and the third crankpin 140)are positioned approximately in phase with one another (i.e.,approximately positioned for in-phase rotation about the crankshaft axisof rotation) so that a single rotational crankshaft position causes thepiston that is coupled to the first crankpin 120 and the piston that iscoupled to the third crankpin 140 to both be positioned at or near thetop of their strokes. Accordingly, as the crankshaft 100 rotates throughits range of crankshaft rotational positions, the piston that is coupledto the first crankpin 120 and the piston that is coupled to the thirdcrankpin 140 both reach the top of their stroke at approximately thesame crankshaft rotational position. The combustion events for the firstand third cylinders occur in alternating cyclic rotations of thecrankshaft such that combustion events associated with the 4-strokecylinders are approximately evenly spaced apart.

In accordance with this embodiment, the second crankpin 130 is coupled,through a connecting rod (not shown), to a piston (not shown) that isdisposed in the cylinder 16 that is disposed between the two 4-strokecylinders 14. That cylinder is configured to operate on a four-strokecombustion cycle. Thus, as crankshaft 100 rotates about the crankshaftaxis of rotation 118, the piston that is coupled to the second crankpin130 interacts with working fluid (i.e., fuel, air and EGR mixture) inthe second cylinder 16, which encounters a combustion event once forevery 360 degrees of crankshaft rotation.

In accordance with this embodiment, the second crankpin 130 (i.e., thecrankpin associated with the 2-stroke cylinders 16) is positionedapproximately 180 degrees out of phase from the first crankpin 120 andthe third crankpin 140. Accordingly, the piston that is coupled to thesecond crankpin 130 reaches the top of its stroke at a rotationalcrankshaft position approximately 180 degrees apart from the rotationalcrankshaft position associated with the top of stroke of the pistoncoupled to the first crankpin 120 and the rotational crankshaft positionassociated with the top of stroke of the piston coupled to the thirdcrankpin 140. Accordingly, the combustion events for the second cylinderoccur in every cyclic rotation of the crankshaft, spaced approximatelyevenly between combustion events associated with the 4-stroke cylinders.Thus, the second crankpin 130 is coupled with the piston associated withthe 2-stroke cylinder 16 and is oriented symmetrically (i.e. slightlymore or less than 180 degrees of rotation of the crankshaft) to thefirst and third crankpins.

In an exemplary embodiment, the axes 122, 132, 142 of all threecrankpins are disposed, more or less, in a single plane 180, and theaxis of rotation 118 of the crankshaft is also disposed, more or less,in approximately the same plane 180. In another exemplary embodiment,the axis of the first crankpin 122 is approximately, more or less,co-linear with the axis of the third crankpin 142.

In the illustrated embodiment, the three crankpins form a crankpingrouping in which the outer crankpins are positioned near a firstapproximate angular location for in-phase rotation about the crankshaftaxis of rotation and the inner crankpin is positioned approximately 180degrees apart from the first approximate angular location. It should benoted, however, that other arrangements are contemplated such as anarrangement wherein three crankpins form a crankpin grouping in whichtwo adjacent crankpins are positioned near a first approximate angularlocation for in-phase rotation about the crankshaft axis of rotation,and the remaining crankpin (which is not positioned between the twoadjacent crankpins) is positioned approximately 180 degrees apart fromthe first approximate angular location.

It should be noted that the strokes of the outer crankpins of thecrankpin grouping may be configured to be greater than, less than, orequal to the stroke of the inner crankpin as desirable to suit specificneeds of the engine. For example, where the 2-stroke (i.e., 180 degreeout of phase) cylinder is utilized to supply EGR to two or more 4-strokecylinders, it may be desirable to increase or decrease the ratio of EGRto be supplied to the four-stroke cylinders. In an exemplary embodiment,the proportion of EGR can be modified by increasing or decreasing thestroke (i.e., range of piston travel) associated with the 2-strokecylinder relative to that of the 4-stroke cylinders.

In an exemplary embodiment, the crankpin for the 2-stroke, dedicated EGRcylinder 16 may be oriented symmetrically (i.e. slightly more or lessthan 180 degrees of rotation of the crankshaft) to the crankpins of the4-stroke cylinders 14 in order to optimize the timing of the delivery ofthe EGR 46, FIG. 1, or combustion charge 82, FIG. 2, to the 4-strokecylinders 14. In the embodiments illustrated, in the 3 cylinder in-lineinternal combustion engine 10, two cylinders can operate on a 4-strokecycle with the remaining cylinder operating on a 2-stroke cycle tosupply recirculated exhaust gas 46 or combustion charge 82 to the4-stroke cylinders. Such a configuration will yield 4 substantiallyevenly spaced firing or combustion events in about 720 degrees ofcrankshaft rotation and yield near 4-cylinder engine performance andcombustion smoothness in a in a 3-cylinder engine package 10.

FIG. 7 and FIG. 8 show exemplary relationships 300 between piston strokeand crankshaft rotational position for exemplary engine rotating groups.In an exemplary embodiment, at a first crankshaft rotational position of0 degrees, a first crankpin 320 and a third crankpin 340 are disposed ina position associated with the top of the stroke (TDC) of their coupledpistons. At this approximate rotational position (with variationsassociated with advancement or retarding of the ignition timing), afirst combustion or firing event 370 occurs in the cylinder associatedwith the first crankpin 320. At approximately the same crankshaftrotational position, a second crankpin 330 is disposed in a positionassociated with the bottom of the stroke (BDC) of its coupled piston.

At a second crankshaft rotational position approximately 180 degreesapart from the first crankshaft rotational position, the first crankpin320 and the third crankpin 340 are disposed in a position associatedwith the bottom of the stroke (BDC) of their coupled pistons. Atapproximately the same crankshaft rotational position, the secondcrankpin 330 is disposed in a position associated with the top of thestroke (TDC) of its coupled piston. At this approximate rotationalposition (with variations associated with advancement or retarding ofthe timing of the ignition timing), a second combustion or firing event350 occurs in the cylinder associated with the second crankpin 330.

Completing a first revolution of the crankshaft at a rotational positionof 360 degrees, the first crankpin 320 and the third crankpin 340 are,again, disposed in a position associated with the top of the stroke(TDC) of their coupled pistons. At this approximate rotational position(with variations associated with advancement or retarding of theignition timing), a third combustion or firing event 360 occurs in thecylinder associated with the third crankpin 340. At approximately thesame crankshaft rotational position, the second crankpin 330 is, again,disposed in a position associated with the bottom of the stroke (BDC) ofits coupled piston.

At a fourth crankshaft rotational position approximately 540 degreesfrom the first crankshaft rotational position, the first crankpin 320and the third crankpin 340 are, again, disposed in positions associatedwith the bottoms of the strokes (BDC) of their coupled pistons. Atapproximately the same crankshaft rotational position, the secondcrankpin 330 is, again, disposed in a position associated with the topof the stroke (TDC) of its coupled piston. At this approximaterotational position (with variations associated with advancement orretarding of the ignition timing), a combustion or firing event 350occurs in the cylinder associated with the second crankpin 330.

Completing a second revolution of the crankshaft with a total crankshaftrotation of 720 degrees, the first crankpin 320 and the third crankpin340 are, again, disposed in a position associated with the top of thestroke (TDC) of their coupled pistons. At this approximate rotationalposition (with variations associated with advancement or retarding ofthe ignition timing), a combustion or firing event 370 occurs in thecylinder associated with the first crankpin 320. At approximately thesame crankshaft rotational position, the second crankpin 330 is, again,disposed in a position associated with the bottom of the stroke (BDC) ofits coupled piston. Thus, a “near-even fire” combustion sequence isfacilitated, whereby, in the case of the 3-cylinder internal combustionengine 10, four nearly evenly spaced firing events occur in about 720degrees of rotation of the crankshaft.

In the embodiments illustrated and described, the internal combustionengine 10 will package in the space of a 3-cylinder, in-line engine butwill deliver near 4-cylinder performance. Four firing impulses or eventswill allow the engine to enjoy a lowered idle speed from about 1000revolutions per minute (“RPM”) to about 750 RPM due to smoother feedbackto the vehicle, or other installation, resulting in lower fuelconsumption. In addition, the output constituents 38 (i.e. exhaust gas)of the 2-stroke, dedicated EGR cylinder 16 are “post-processed” by the4-stroke cylinders 14 allowing the 2-stroke, dedicated EGR cylinder 16to be operated richer than stoichiometry without an adverse impact ontailpipe emissions 50. This allows the 2-stroke, dedicated EGR cylinder16 to be optimized as a supplier of EGR diluent to the 4-strokecylinders 14.

The operation of the internal combustion engine 10 is relativelystraight forward and the configuration of the 2-stroke, dedicated EGRcylinder 16 may comprise a number of 2-stroke designs. For instance, inan exemplary embodiment, a “uniflow” design may be implemented whichwill utilize exhaust valves in fluid communication with the exhaustports 40. Intake ports 34 may be dispensed with in exchange for intakeports (not shown) at the bottom of the cylinder 16. The cylinder 16 maybe crankcase scavenged but also maybe scavenged with pressurized airfrom the compressor 20. In the exemplary embodiments illustrated inFIGS. 1 and 2, the layout of the 2-stroke, dedicated EGR cylinder 16 issimilar to that of a 4-stroke engine in its configuration. The primarydifference between 2-stroke and 4-stroke operation of the cylinder 16 isin the valve-injector-spark timing relative to the position of theengine crankshaft (not shown). This configuration benefits fromcompressed combustion air 18, FIG. 1, or the compressed combustioncharge 82, FIG. 2, delivered by compressor 20. In an exemplaryembodiment, a compressor 20 may be dispensed with when the exhaust gastreatment system 54 and the timing of the exhaust valves of the 2-strokecylinder 16 can be controlled to create “auto-scavenging” of exhaust gasfrom the cylinder 16.

As indicated above, the invention is applicable to various engineconfigurations. In a V-configured engine, such as a V-6 engine, fourcylinders can operate on a 4-stroke cycle with the remaining twocylinders operating on a 2-stroke cycle to supply recirculated exhaustgas to the 4-stroke cylinders. Such a configuration will yield 8 firingor combustion events in about 720 degrees of crankshaft rotation andyield near V-8 engine performance in a V-6 package. In the exemplaryembodiment of FIG. 3, the V-6 configured internal combustion engine 10Cis configured such that two cylinders (4 and 6 in the engineillustrated) on a first cylinder bank 90 are operated on a 2-strokecycle. The remaining cylinders 1, 2, 3 and 5, which are located invarious locations on both first cylinder bank 90 and second cylinderbank 92, operate on a 4 stroke cycle. This configuration is useful inorder to optimize the firing order of the cylinders 14, 16 as well asthe delivery of recirculated exhaust gas 46 from the 2-stroke cylinders16 to the 4-stroke cylinders 14.

In the exemplary embodiment of FIG. 4, the V-6 configured internalcombustion engine 10B is configured such that two cylinders (2 and 4 inthe engine illustrated) on first cylinder bank 90 are operated on a2-stroke cycle. The remaining cylinders 1, 3, 5 and 6, which are locatedin various locations on both first cylinder bank 90 and a secondcylinder bank 92, operate on a 4 stroke cycle. This configuration isalso useful in order to optimize the firing order of the cylinders 14,16 as well as the delivery of recirculated exhaust gas from the 2-strokecylinders 16 to the 4-stroke cylinders 14.

The invention has been described above primarily with reference to itsapplication in a 3-cylinder or a 6-cylinder engine. It should be clearto one skilled in the art of internal combustion engines that engines ofother cylinder numbers, and varied configurations, can easily beenvisaged and that the invention should not, and can not be limited tothose examples provided herein.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed, but that theinvention will include all embodiments falling within the scope of thepresent application.

What is claimed is:
 1. A crankshaft for an internal combustion enginecomprising: at least four main journals aligned on a crankshaft axis ofrotation; and at least three crankpins, each disposed about a respectivecrankpin axis and positioned between the main journals; each of therespective crankpin axes being oriented parallel to, and spaced radiallyfrom, the crankshaft axis of rotation; each of the crankpins beingjoined to a pair of crank arms for force transmission between thecrankpin and the pair of crank arms; each pair of crank arms beingjoined to a respective main journal for transmitting torque between thepair of crank arms and the main journal; two of the crankpins beingpositioned substantially in phase with one another and a third crankpinbeing positioned approximately 180 degrees apart from the at least twocrankpins.
 2. A crankshaft as in claim 1, wherein the at least threecrankpins form a crankpin grouping in which the outer crankpins arepositioned near a first approximate angular location for in-phaserotation about the crankshaft axis of rotation.
 3. A crankshaft as inclaim 2, wherein the inner crankpin is positioned approximately 180degrees apart from the first approximate angular location.
 4. Acrankshaft as in claim 1, wherein the at least three crankpins form acrankpin grouping in which two adjacent crankpins are positioned near afirst approximate angular location for in-phase rotation about thecrankshaft axis of rotation.
 5. A crankshaft as in claim 4, wherein theremaining crankpin is positioned approximately 180 degrees apart fromthe first approximate angular location.
 6. A crankshaft as in claim 2,wherein the crankpin grouping includes four main journals.
 7. Acrankshaft as in claim 6, wherein each of the crankpins of the crankpingrouping is disposed between a pair of main journals.
 8. A crankshaft asin claim 2, wherein the inner crankpin of the crankpin grouping isoriented symmetrically to the outermost two crankpins of the crankpingrouping.
 9. A crankshaft as in claim 2, wherein the three crankpins ofthe crankpin grouping and the axis of rotation of the crankshaft are alldisposed approximately in a single plane.
 10. A crankshaft as in claim2, wherein the axes of the outer crankpins of the crankpin grouping areapproximately co-linear.
 11. A crankshaft as in claim 2, wherein thestrokes of the three crankpins of the crankpin grouping areapproximately equal.
 12. A crankshaft as in claim 2, wherein the strokesof the outer crankpins of the crankpin grouping are greater than thestroke of the inner crankpin.
 13. A crankshaft as in claim 2, whereinthe strokes of the outer crankpins of the crankpin grouping are lessthan the stroke of the inner crankpin.
 14. A rotating group for a threecylinder internal combustion engine, the rotating group comprising:three pistons, each associated with a respective cylinder and connectedthrough a respective connecting rod to a respective crankpin, thecrankpins being disposed on a single crankshaft; wherein the crankshaftcomprises: at least four main journals aligned on a crankshaft axis ofrotation; and at least three crankpins, each disposed about a respectivecrankpin axis and positioned between the main journals; each of therespective crankpin axes being oriented parallel to, and spaced radiallyfrom, the crankshaft axis of rotation; each of the crankpins beingjoined to a pair of crank arms for force transmission between thecrankpin and the pair of crank arms; each pair of crank arms beingjoined to a respective main journal for transmitting torque between thepair of crank arms and the main journal; and at least two of thecrankpins being positioned substantially in phase with one another and athird crankpin being positioned approximately 180 degrees apart from theat least two crankpins.
 15. A rotating group as in claim 14, wherein theat least three crankpins form a crankpin grouping in which the outercrankpins are positioned near a first approximate angular location forin-phase rotation about the crankshaft axis of rotation.
 16. A rotatinggroup as in claim 15, wherein the inner crankpin is positionedapproximately 180 degrees apart from the first approximate angularlocation.
 17. A rotating group as in claim 15, wherein each of thecrankpins of the crankpin grouping is disposed between a pair of mainjournals.
 18. A crankshaft as in claim 15, wherein the three crankpinsof the crankpin grouping and the axis of rotation of the crankshaft areall disposed approximately in a single plane.
 19. A crankshaft as inclaim 15, wherein the strokes of the outer crankpins of the crankpingrouping are greater than the stroke of the inner crankpin.
 20. Acrankshaft as in claim 15, wherein the strokes of the outer crankpins ofthe crankpin grouping are less than the stroke of the inner crankpin.